Petroleum recovery is typically accomplished by drilling into a petroleum containing formation and utilizing one of the well known methods for the production of petroleum. However, these recovery techniques may recover only a minor portion of the petroleum present in the formation particularly when applied to formations containing viscous petroleum. In such cases, secondary recovery methods, such as water flooding, steam injection, gas flooding and combinations thereof, may be used to enhance petroleum recovery. Underground oil-containing formations also contain clay or clay like bodies and treatment with water or steam generally results in swelling of the clay by absorption of the water, with the result that the water permeability of a formation is decreased. The decrease in the permeability of the formation causes a reduction in the amount of oil which may be recovered by secondary recovery operations.
Methods for enhancing the recovery of petroleum from underground formations are known. The production of petroleum may be improved or reinstated from formations which have been partially depleted by primary recovery techniques or where communication between an injection well and a recovery well has been restricted by the swelling of water sensitive clays in the formation. Methods include injecting an aqueous composition into a first well to force residual petroleum in an underground formation through the formation and out of one or more recovery wells. A water dispersible polymeric material such as a hydrated polysaccharide may be included in the aqueous composition to increase viscosity when the residual petroleum is viscous.
The injected aqueous compositions generally have a lower viscosity at reservoir conditions than the viscosity of the formation crude which it is intended to displace, making it less effective. Various additives, such as polymers, have been proposed to increase the viscosity of the injected fluid in order to improve the efficiency.
These aqueous compositions often contain dissolved or entrained air which increases the rate of corrosion and deterioration of metal surfaces in the drill string and associated equipment. Oxygen scavenger additives such as sodium dithionite and mixtures thereof have been used with some success. Sodium dithionite is available in powder or liquid form but is difficult to handle and presents a fire hazard when exposed to the atmosphere. When used in powder form, the sodium dithionite is typically suspended in a liquid carrier, insulating the oxygen reactive materials from the atmosphere. When used in liquid form, the sodium dithionite must be transported under climate control.
U.S. Pat. No. 4,458,753 discloses a method of tertiary oil recovery from petroleum formations at elevated temperature by injecting a substantially oxygen-free aqueous saline solution of a water-soluble polysaccharide biopolymer treated at pH of at least 5 by addition of alkali metal borohydride as a viscosity stabilizer.
U.S. Pat. No. 4,218,327 discloses the use of oxygen scavengers and alcohols to stabilize water-soluble anionic polysaccharide (Xanthan gum polymer) solutions from loss of viscosity at elevated temperatures.
Accordingly, there exists a need to provide a stable sodium dithionite composition for use in industrial applications while minimizing the impact to the environment and eliminating operator's exposure.